The QD factor \(f_g^{u}\)  defines an approximate closure for the group LOQD equations
providing further data compression of intensities and the next level of reduction of dimensionality for the TRT problem.
Hereafter we refer to this ROM as the QD-PODG model, whose iterative algorithm for solving TRT problems is outlined in Algorithm REF .
Temporal discretization of the LOQD and MEB equations (Eqs. (REF ), (REF ), and (REF )) is based on the BE time integration method.
The multigroup LOQD
equations are discretized in space by means of a second-order finite volume (FV) method [1]}.
The spatial discretization of the grey LOQD equations is algebraically consistent with the discretized multigroup LOQD equations.
